Furnace for separation of volatile constituents of ores

ABSTRACT

A gravity-flow, mercury ore reduction furnace having a hollow, vertical firebrick housing, an ore-feed hopper on its upper end, a vibratory ore-discharge conveyor on its lower end, an elongated heating element extending upwardly through the housing in a central plane and defining a serpentine passage for fire gases supplied to its lower end, and means for withdrawing mercury vapor from the lower portion of the furnace. In one form, the heating element is a continuous tubular coil, and in a modified form, the lower portion of the element is a sealed box structure of high-temperature sheet material having partitions forming vertically spaced galleries for a serpentine flow of gases through the box structure and into a coil forming the upper portion of the element, some of the partitions being made hollow and used for vapor withdrawal.

United States Patent 1191 Gardiner Apr. 2, 1974 FURNACE FOR SEPARATION OF VOLATILE CO NSTITUENTS OF ORES Philip M. Gardiner, Bishop, Calif.

Inventor:

Primary Examiner-Gerald A. Dost Attorney, Agent, or Firm-Fulwider Patton Rieber Lee & Utecht [57] ABSTRACT I A gravity-flow, mercury ore reduction furnace having a hollow, vertical firebrick housing, an ore-feed hopl l Filedl g- 1972 per on its upper end, a vibratory ore-discharge con- I 77 veyor on its lower end, an elongated heating element [2 1 NO 2839 extending upwardly through the housing in a central plane and defining a serpentine passage for fire gases [52] U .S. Cl. 266/17 supplied to its lower end, and means for withdrawing [51] Int. Cl C22b 5/16 m r ury vapor from the lower portion of the furnace. [58] Field of Search 75/71, 81, 86, 88; ln one form, the heating element is a continuous tubu- 266/15-17, 19, 24, 25 lar coil, and in a modified form, the lower portion of the element is a sealed box structure of high- [56] References Cited temperature sheet material having partitions forming UNITED STATES PATENTS vertically spaced galleries for a serpentine flow of 3,025,043 3/1962 Ruelle et al 266 15 gases thmugh structure'and mm a form 708,438 9 1902 Wetherill 266 19 95 the PP P n of t element, some of the Pf- 1,222,251 4/1917 Whitton 75/81 Hons g made hollow and used for vapor With- FOREIGN PATENTS OR APPLICATIONS drawal' 27,708 3/1917 Norway 266/19 10 Claims, 6 Drawing Figures L l, y

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1. 4] 4 E a} 4 4 1 r L9 5 s r ark. saw/Q PAIENTEDAPR 21914 3801081 sum 2 BF 2 FURNACE FOR SEPARATION OF VOLATILE CONSTITUENTS OF ORES BACKGROUND OF THE INVENTION This invention relates to the separation of materials by heating, and has particular reference to a reduction furnace for heating an ore bearing a relatively volatile material until the volatile material is driven off as a vapor.

Furnaces of this type are used for recovering a variety of materials from their ores, a specific example for which the present furnace was primarily designed being the recovery of mercury, or quicksilver, from cinnabar ores. Several types of furnaces are presently available and in use for this purpose, perhaps the best known being the Herreshoff (multiple hearth) and Gould (rotary) furnaces. Other examples are shown in U.S. Pat. Nos. 2,311,648, 2,302,841, 2,497,096 and 2,939,695.

Basically, in all of these furnaces, the ore is introduced in finely crushed form into a heating chamber and subjected to a temperature sufficiently high to cause the mercury to be released as a gas, a temperature above 1082.3 degrees F., and usually between 1 150 and 1250 degrees F., or higher. In the rotary type of furnace, this is accomplished by blasting the ore with impinging fire gases as the ore travels in a rotating shell. in the multiple-hearth type, the ore is heated by fire gases while being transferred by rakes or plows along a series of vertically spaced hearths, dropping from one hearth to the next in passing through the furnace. The multiple-hearth furnaces are characterized by greater fuel economy than the rotaries, but higher construction and engineering costs, and both types produce very large volumes of fire gases in which the mercury to be recovered is mixed, requiring large, cumbersome and expensive systems for cooling the fire gases and condensing the mercury for recovery thereof. Of course, the mercury can be contaminated with constituents such as soot from the fire gases, and the latter can be discharged into the atmosphere with mercury contamination, if condensation is less than perfect.

Multiple-hearth furnaces are shown in US. Pat. No. 976,175 and in the aforesaid US. Pat. No. 2,302,841, which recognizes and attempts to reduce the problems of contamination of the recovered mercury. The furnaces in US. Pat. Nos. 2,311,648 and 2,497,096 illustrate other attempts to reduce or eliminate contamination while providing for effective separation and recovery of mercury. In each case, however, the resulting furnace structure is relatively complex, and thus expensive to construct, and the fuel economy achieved is questionable.

SUMMARY OF THE PRESENT INVENTION The present invention resides in an ore reduction furnace which is of relatively simple, compact, and inexpensive construction and is capable of processing ore at a relatively high rate per unit of cost. Moreover, the fire gases are introduced into the ore in a highly effective manner, yet isolated from the released vapor throughout the process, thus preventing contamination and simplifying the condensation operation. Optimum utilization of the heat of fire gases is achieved for optimum heating economy and minimum thermal pollution, and both withdrawal of separated gases and control of ore feed rates are accomplished in effective and simple manners.

More specifically, and as illustrated in the preferred embodiments shown herein, the improved furnace comprises an elongated housing of refractory material having open upper and lower ends and defining an elongated, hollow furnace chamber in which an upright, elongated heating element is mounted in spaced relation withthe walls of the housing. The heating element defines a sealed, serpentine path for a fluid heating medium such as fire gases from an external source, and also divides the furnace chamber into two flow passages for ore which is delivered to the upper end to gravitate through the chamber on both sides of the heating element for discharge at a controlled rate through the lower end.

With this arrangement, the fire gases are effectively isolated from the ore and the mercury vapor released, and the ore is heated progressively during its downward flow through the furnace, the temperature building up progressively from the upper, discharge end of the heating element toward the lower, input end. At a preselected and controllable level in the lower portion of the furnace, the ore attains the separation temperature, and mercury released as vapor is withdrawn from the ore through vacuum conduits projecting into the separation zone and communicating with the spaces on both sides of the heating element.

To define the serpentine path for fire gases, the heating element preferably comprises an elongated tube or coil of heat-conducting material that extends back and forth in a series of U-shaped bends that are connected by straight sections of the tube extending transversely of the flow paths. This provides for high residence time of the gases in the tube, and in heating relation with the ore, so that virtually all of the available heat can be imparted to the ore before the gases leave the furnace. The ore is at substantially ambient temperature near the upper or outlet end of the element, for effective heat exchange between the element and the ore in the upper portion of the furnace, so that the fire gases are discharged at a temperature at or near the ambient temperature.

Mercury vapor and the high temperature levels in the lower portion of the furnace cooperate to form a corrosive atmosphere that is highly destructive of most materials, and presently available materials that are resistant to this atmosphere over prolonged periods of use are not easily formed into a serpentine tubular form. For

this reason, the portion of the heating element in the zone of highest temperatures, the separation zone, may be of special construction permitting the use of sheet material such as carborundum that is not readily and economically available in serpentine tubular form, yet is highly resistant to the furnace atmosphere. Sheet material of this type is used to fabricate a hollow box structure that is sealed to isolate the fire gases from the ore and vapor, with internal partitions dividing the box into a series of laterally elongated, vertically spaced galleries which communicate with each other through connecting ports alternating upwardly from one side of the structure to the other. A shortened tubular element is connected to the upper gallery to carry the fire gases through the cooler upper zone of the furnace, the box structure constituting a highly resistant extension of the tubular element at the high-temperature, inlet-end portion thereof.

are formed as evacuating chambers having perforations v communicating with the interior of the housing to draw vapor therefrom through the sidewalls of the structure.

The improved furnace structure lends itself to accurate and variable control of the feed rate of ore to achieve optimum heating. A variable discharge device such as a vibratory conveyor, controls the discharge rate, and sensors are provided, most importantly in the separation zone, to measure the temperature of the ore. By varying the discharge rate to increase or reduce the feed rate through the furnace, the temperature in the separation zone can be held at, or very close to, the op timum.

Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.

I BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary perspective view, partly schematic in form and partly broken away and shown in cross-section, of an ore reduction furnace embodying the novel features of the present invention;

FIG. 2 is a view of the furnace of FIG. 1 taken primary in a vertical plane through the furnace, central portions being removed for compactness;

FlG. 3 is an enlarged fragmentary view, partly in cross-section, taken from the side of the heating element, generally along line 33 of FIG. 4;

FIG. 4 is an enlarged fragmentary view taken substantially along 4-4 of FIG. 1;

FIG. 5 is an enlarged fragmentary perspective view of a box structure usable as part of the heating element in a modified form of the invention.

FIG. 6 is an enlarged fragmentary cross-sectional view taken along line 6-6 of FIG. 5.

' DETAILED DESCRIPTION As shown in the drawings for purposes of illustration, the invention is embodied in a furnace l0 designed primarily for the removal of mercury from cinnabar ore which is introduced into the furnace through a hopper 11 on the upper end thereof, and flows downwardly through the hollow interior chamber 12 of the furnace to be heated by a heating element 13 therein to the temperature at which the mercury separates as a vapor. The vapor is drawn off by withdrawal means indicated generally by the number 14, and the remaining ore residue, called calcines," is discharged from the lower end of the furnace by means of a conveyor 15.

The body of the furnace may be simply a housing laid up of suitable refractory material such as firebricks, and herein is of rectangular horizontal crosssection and has an open upper end on which the hopper 11 is mounted, beneath a suitable ore-feeding conveyor 17, and an open lower end to which a discharge bin 18 is attached to funnel the ore residue into the discharge ferredform being a vibratory conveyor of conventional construction that is selectively adjustable to provide a variable discharge rate.

In accordance with the present invention, the interior chamber 12 of the furnace 10 is simply an upright through passage for the ore that is introduced through the hopper l1, and the heating element 13 is positioned in the chamber between the walls of the housing to divide the chamber, in effect, into two flow paths for the gravitation of ore past the element, in heat conducting contact therewith. The heating element defines a sealed serpentine passage for a fluid heating medium,

typically fire gases, and has an inlet end portion 19 near the lower end of the furnace housing, connected to a suitable external source 20 of tire gases, and an outlet end portion 21 near the upper end thereof.

With this arrangement, fire gases are introduced into the heating element 13 at the lower end, at a suitable inlet temperature that may be as high as 2200 degrees F and flow upwardly through the element to heat the gravitating ore in the housing on both sides of the element and around the side edges thereof, the fire gases being confined in the element and thus isolated from the ore and from the vapor released therefrom. The gravitating ore is progressively heated as it moves downwardly through the chamber 12, and the gases, in turn, are progressively cooled as they rise through the heating element. By correlating the various flows, the temperatures can be controlled to insure that the ore temperature is elevated to the proper level for separation of the mercury in the lower portion of the furnace, and that most or all of the available heat is extracted from the fire gases before they exit from the upper end of the furnace.

More specifically, the heating element 13 shown in FIGS. 1 through 4 comprises an elongated and continuous tube of heat-resistant material having a plurality of vertically spaced generally horizontal sections 22 extending transversely of the furnace, generally in a central vertical plane, and connected at their ends by U- shaped bends 23 alternating at the opposite ends of the straight sections to form the continuous serpentine passage within the heating element. The lowermost straight section 22 projects through the right-hand wall 24 of the housing and is connected to the source 20, and the uppermost straight section is connected to an exit section 25 of the tube which leads out of the hopper 1 1 over the left-hand wall 27 of the housing to a disposal system (not shown) for the spent gases.

The heating element 12 may be made in sections for convenience and economy in fabrication, and different materials may be used for different temperature zones within the furnace. For example, the upper two-thirds may be composed of an alloy that is resistant to lower temperatures, such as 304 stainless steel or inconel,

and the lower one-third may be composed of more ex- 7 pensive material suitable for higher temperatures, such as titanium or carborundum.

- It will be apparent that this heating element 13 will convey the tire gases back and forth, transversely of the fumace chamber 12 between the right and left-hand walls 24 and 27 of the housing, in spaced relation with the front and rear walls 28 and 29, while progressing upwardly through the chamber 12 in substantially equally spaced relation with all of the walls. Although the element effectively divides the chamber into two primary flow paths along the front and rear walls, it can be seen that the mass of ore in the furnace, including the portions in the spaces at the longitudinal edges of the element formed by the bends 23, will be generally rectangular in horizontal cross-section.

Accordingly, the horizontal sections 22 of the element 13 define elongated, laterally extending galleries for the lateral flow of heating gases transversely of the vertically elongated furnace chamber 12, and provide for prolonged residence time of the fire gases in the chamber 12 between the upper and lower ends thereof. The flow rate through the heating element will depend upon the pressure differential across its ends, which differential is regulated by means of a negative pressure source (not shown) for applying suction to the upper end to draw the gases through the element. 'This prolonged residence time and back and forth transmission of the gases through the furnace, taken with increased height of the furnace, make it possible to effect optimum transfer of available heat to the ore.

Removal of mercury vapor is effected by the withdrawal means 14, which herein comprise a plurality of pick-up tubes projecting into the furnace chamber 12 through the left-hand wall 27 of the housing, in the lower portion thereof where the temperature of the ore is the highest. The upper pick-up tube should be adjacent the level where the ore can be expected to first attain the critical temperature of 1082.3 degrees, somewhat above the lower end of the heating element 13, and the additional tubes are spaced below this level in the zone where most of the separation will occur, as the mass of ore is brought up to the separation temper ature.

Herein, as shown in FIGS. 1 and 2, three pick-up tubes 30 project into the high-temperature zone through the left-hand wall 27, and have perforated inner end portions which are disposed between adjacent straight sections 22 of the heating element 13, out of the main streams of ore passing through the furnace. A fourth pick-up tube projects into the bin 18 beneath the housing, to collect any vapors that may be separated from the ore residue in the bin.

All four of these pick-up tubes 30 are connected at their outer ends to a line 31 leading to a suction pump (not shown) in the condensing system serving the furnace. Thus, suction applied through the perforations in the tubes draws the mercury vapor into the pick-up tubes, from the ore on both sides of the heating element 13, and carries the vapor through the line 31 to the condensing system.

Preferably, an elongated shield 32 (see FIGS. 3 and 4) of arcuate cross-section is disposed over each of the pick-up tubes 30 to deflect the passing ore away from the tubes. The perforations may be simply drilled holes sufficiently small to prevent any substantial removal of solid particles with the vapor, the holes being shown in FIGS. 3 and 4 as extending into the tube from all sides thereof. If desired, the holes can be limited to the upper area of the tubes to further reduce the likelihood of collection of solid particles. The shields 32 may be supported on the tops of the tubes 30 by small fasteners For proper control of the feed rate of ore through the furnace, it is important toknow the temperature levels that actually are attained, particularly in the separation zone of the furnace. For this purpose, at least one conventional temperature probe 34 (FIG. 2) is positioned in the furnace to sense the temperature in the separation zone and produce a signal indicative of this temperature. In addition, for check purposes, probes 35, 37, and 38 may be provided in the hopper 11, in the upper zone, and in the bin 18, respectively.

Shown in FIGS. 5 and 6 is a modification 13 of the lower portion of the heating element 13, this modification being preferred for increased durability of the-element with presently available and economically feasible materials. As previously suggested, the high temperatures in this zone, combined with the corrosive nature of the atmosphere in the furnace, can result in relatively rapid deterioration of many materials that could otherwise be used economically to form a serpentine tube. Materials such as carborundum which have the necessary resistance for long service life are not economically available in tube form.

As shown in FIGS. 5 and 6, this problem can be solved by fabricating the lower portion 39 of the heating element 13 in the form of a sealed box structure having front, rear, top, bottom and side walls 40, 41, 42, 43 and 44, respectively, composed of sheet material, such as carborundum. A plurality of partitions 45 composed of the sheet material are positioned in the box structure in vertically spaced relation, and are shorter than the width of the structure to leave gaps 47 between the ends of the partitions and the side walls 44, the gaps alternating from one side to the other within the box structure to define a vertical series of elongated galleries communicating with each other at alternating ends. Thus, the box structure defines a shortened serpentine passage similar to the passage defined by the tubular element in FIGS. 1 and 2.

The outside walls of the box structure 39 may be secured and sealed together in various ways, so that the galleries therein are effectively isolated from the interior of the furnace. The partitions 45 need not be sealed against the walls, because minor leakage around them is no problem. Simple abutments (not shown) can be secured to the inner sides of the walls to serve as supports for the partitions, or the partitions can be welded or otherwise bonded to the walls of the box structure.

Since it is only roughly the lower one-third of the furnace in which the highest temperature range occurs, the box structure 39 can be used in this area, and connected to a tubular extension 48, similar to the heating element 13 shown in FIGS. 1 and 2, for carrying the fire gases through the remainder of the furnace. Part of such an extension is shown in FIG. 5, having a lower end connected to the top wall 42 of the structure by a suitable fitting 49, above the end of the uppermost gallery remote from the port 47 for admitting gases from the next lower gallery into the uppermost gallery. Fire gases are admitted into the lowest gallery through a pipe 50 connected between the source of fire gases and the lower end portion of one sidewall 44 of the box structure, the end of the lowest gallery remote from the port 47 through which the fire gases rise to the next gallery. It will be seen in FIG. 5 that the thickness and width of the box structure can be approximately the same as the thickness and width of the tubular upper portion 48 of the modified heating element.

In a furnace equipped with the modified heating element l3, mercury vapor separated from the ore advantageously is withdrawn from the interior of the furnace through the box structure 39, which is positioned in the zone' of highest temperatures where most of the separation occurs. As shown in FIGS. 5 and 6, this is accomplished by making one or more, herein two, of the partitions 45 hollow (these partitions being indicated by the reference numbers 45a), and forming pick-up holes 51 in the front and rear walls 40 and 41 of the box structure to communicate between the interior of the furnace and the chambers 52 defined in the partitions, these partitions being welded to the walls of the box structure 39 and sealed from the galleries, so as to be isolated from the fire gases. Two pick-up tubes 53 are connected to a line 54 leading to a source of negative pressure, to apply-suction to the chambers 52 and, through the pick-up holes 51, to the interior of the furnace in the separation zone.

While the pick-up tubes may be simply connected to the left-hand sidewall 44 of the box structure 39 to communicate with the chambers 52 through holes in this wall, they preferably project into the chambers 52 and haveperforated inner end portions through which the suction is applied. As shown in FIG. 6, perforations 55 preferably are formed in the top portion of each tube, to avoid direct, straightline flow paths to the holes 51, and the latter are outwardly tapered to relatively small outer ends to minimize the amount of particulate matter that will be drawn into the chamber with the mercury vapor.

Operation of the furnace is the same, whether the heating element is in the form 13 shown in FIGS. 1 and 2 or in the modified form 13' shown in FIGS. 5 and 6. An initial charge of crushed ore is fed into the hopper 11 by the conveyor 17 to fill the furnace on both sides of the heating element, and the source 20 of fire gases is activated to begin supplying fire gases to the heating element. Start-up time with the improved furnace is relatively short, as compared with prior furnaces. For example, a large multiple-hearth furnace may require as long as 24 hours preparation for start-up, whereas the present furnace will be ready for operation after a warm-up period as short as 20 minutes.

With the discharge end of the heating element connected to a vacuum source for drawing the fire gases through the furnace, and the vapor pick-up tubes connected to a vacuum source for drawing mercury vapor from the separation zone of the furnace, the separation and collection of mercury will proceed as soon as part of the ore is heated to the separation temperature of 1082.3 degrees F. As mercury vapor is released, it is sucked out of the ore through the pick-up tubes, and delivered to the condensation system wherein it is collected. When all of the ore in the separation zone has been heated to above the separation temperature, as sensed by the temperature probe 34, and the mercury content has been separated and collected, the discharge conveyor 15 can be activated to begin discharging the ore residue from the furnace and causing the ore in the upper portion of the furnace to begin gravitating through the furnace.

As this occurs, the gravitating ore is heated progres sively toward the separation temperature by the heating element and the upwardly flowing fire gases therein. Through proper control of the discharge rate, the progressive temperature rise can be controlled to insure that the ore attains a desired high temperature, well above 1082.3 degrees F., as it passes the probe 34. if, due to variations in the supply temperature of the fire gases, the discharge rate of the conveyor 15, or other variables, the temperature sensed by the probe 34 is either too high or too low, the discharge rate can over, the furnace is easily controlled for optimum ef- 8 be adjusted, either manually or automatically, to obtain a proper feed ratethat will result in the desired temperature at the probe 34. The supply conveyor 17 can be similarly controlled to maintain a supply of ore in the hopper ready for entry into the furnace, for example, by level-sensing means (not shown) in the hopper Accordingly, the furnace 10 can be operated continuously with minimum operator attention and skill. If, on' the other hand, the situation is such that intermittent operation is desired, the furnace can be so operated with a minimum of delay for' intermittent start-ups. This characteristic, plus the simplicity and low cost of the furnace, makes it eminently well suited for relatively small operations.

One furnace of this type that has been designed for relatively small operations has a firebrick housing approximately 10 by 24 inches in cross-section and 60 inches high, with a heating element of one-inch O.D. tubing formed with 16 U-shaped bends on each side, and 33 straight sections. Fire gases are supplied at temperatures on the order of 2000 degrees F., and exit from the upper end of the furnace at temperatures between ambient and degrees F. This furnace is designed to process between three and five tons of ore per day.

It is to be understood that the foregoing figures are intended only for purposes of illustration, and not as limiting in any way. Moreover, it should be noted that the furnace may be constructed with more than one heating element, in a common furnace chamber dimensioned for the larger number of elements, so that ore flows downwardly through the furnace along more than two paths. It two elements are used, ore will be heated between the elements as well as between each element and the adjacent walls of the housing. Thus, the furnace concept lends itself readily to increases in furnace capacity to suit a particular situation.

From the foregoing, it will be evident that the present invention provides an improved furnace for the separation of volatile constituents of ores by heating, which furnace is relatively simple and inexpensive in construction and operation, effectively isolates the tire gases from the ore and theseparated vapor to avoid cross-contamination, and confines the fire gases in the furnace and within the ore for a high residence time, whereby efficiently utilizing the available heat. Morefectiveness in operation, and can be fabricated of mate rials that are durableenough for prolonged life in service use.

It also will be apparent that, while particular embodiments of the invention have been illustrated and described, various modifications maybe made without departing from the spirit and scope of the invention.

I claim:

1. An ore reduction furnace having, in combination:

an elongated, upright housing having refractory walls, open upper and lower ends, and a hollow in-' terior extending between said ends and defining a furnace chamber of elongated rectangular horizontal cross-section; I

a hopper on said upper end for receiving ore to be reduced and having an open bottom for directing the ore into said furnace chamber;

a vertically elongated heating element mounted in said furnace chamber in spaced relation with the walls thereof and extending from adjacent said lower end to adjacent said upper end, said heating element comprising a sealed .box structure of sheet material having partitions defining vertically spaced, elongated galleries communicating at alternating ends to define a serpentine passage extending back and forth in an upright plane, and longitudinally of said elongated cross-section, while progressing upwardly in said plane, from a lower inlet end to an upper outlet end, said passage being sealed and isolated from said furnace chamber, and serving to divide the ore in said chamber generally into two flow paths along opposite sides of said element, at least one of said partitions being hollow and having ports therein communicating with the furnace chamber outside said box structure;

means for supplying fire gases to said heating element at said inlet end and causing the fire gases to flow upwardly through the passage to said outlet end, to heat the ore gravitating along opposite sides of the heating element progressively as the ,ore moves downwardly through said housing, while preventing contamination of said ore by said fire gases and preventing contamination of the fire gases by constituents of the ore;

means at the lower end for removing ore at a controlled rate, thereby to control the rate of flow of ore through said furnace and the period of exposure of the ore to said heating element;

and vapor withdrawal means positioned in said chamber at a predetermined level in said lower portion and communicating with said chamber on both sides of said heating element, but isolated from said passage, for removing vapor separated from said ore by heating, said vapor withdrawal means including at least one perforated pick-up tube disposed within said hollow partition.

2. An ore reduction furnace as defined in claim 1 in which said box structure has holes in its walls opening into the hollow interior of the partition, said holes being tapered from relatively small outer ends to relatively large inner ends.

3. An ore reduction furnace as defined in claim 1 in which said box structure has holes in its walls opening into the hollow interior of the partition, and the pick-up tube therein has perforations which open out of the pick-up tube away from said holes, to avoid straightline flow of vapor to the pick-up tube.

4. An ore reduction furnace having, in combination:

an elongated refractory housing adapted for operation in an upright position and having an inlet opening in its upper end for receiving ore, an elongated hollow interior defining a chamber for the flow of ore downwardly through said housing, and a discharge opening in its lower end;'

an elongated heating element disposed in said housing in spaced relation with the walls thereof and extending from an inlet end adjacent said discharge opening, upwardly through said hollow interior to an outlet end, said housing defining two main flow paths on opposite sides of said heating element for gravity flows of ore introduced through said inlet opening, and said heating element defining a sealed passage isolated from said flow paths for'a fluid low input temperature to a relatively high separa-' tion temperature as the ore approaches said outlet end;

means at said discharge opening for removing ore therefrom at a controlled rate thereby to control the rate of flow of ore along said flow paths and the period of exposure of the ore to said heating element;

and vapor withdrawal means in said housing at a predetermined level in the lower portion of said housing communicating with said hollow interior and both of said flow paths, but isolated from said sealed passage, for removing vapor separated from said ore by heating, said vapor withdrawal means being located substantially closer to said discharge opening than to said inlet opening and including a perforated pick-up member extending transversely across said hollow interior, and means for drawing vapor into said pick-up member from said hollow interior.

5. An ore reduction furnace as defined in claim 4 in which said heating element comprises a continuous tube bending back and forth to form a series of oppositely facing U-shaped bends connected by straight sections of said tube, and in which said pick-up member is an elongated tube having a perforated inner end portion disposed between two of said straight sections.

6. An ore reduction furnace as defined in claim 4 in which at least the lower portion of said heating element is a sealed box structure constructed of sheet material and having flat upright walls in spaced relation with the walls of said housing and vertically spaced partitions mounted between said flat walls and defining a series of vertically spaced, transversely extending galleries, adjacent galleries communicating at alternating ends to carry fire gases back and forth along said serpentine path.

7. An ore reduction furnace as defined in claim 6 in which said perforated pick-up member is disposed within one of said partitions, and communicates with said interior through the sides of said box-like structure.

8. An ore reduction furnace having, in combination:

an elongated, upright housing having refractory walls, open upper and lower ends, and a hollow interior extending between said ends and defining a furnace chamber of elongated rectangular horizontal cross-section;

a hopper on said upper end for receiving ore to be reduced and having an open bottom for directing the ore into said furnace chamber;

a vertically elongated heating element mounted in said furnace chamber in spaced relation with the walls thereof and extending from adjacent said lower end to adjacent said upper end, said heating element defining a serpentine passage extending back and forth within said furnace chamber generally in an upright plane, and longitudinally of said elongated cross-section, while progressing upwardly in said plane, from a lower inlet end to an upper outlet end, said passage being sealed and isolated from said furnace chamber, and serving to divide the ore in said chamber generally into two flow paths along opposite sides of said element;

at least part of said heating element being a sealed box structure of heat-resistant sheet material centrally disposed in the lower portion of said chamber and having vertically spaced partitions defining vertically spaced, transverse'galleries communicating through connecting ports positioned in an alterv nating manner adjacent the opposite sides of said structure to cause said fire gases to flow back and forth while progressing upwardly through the box structure;

means for supplying fire gases to said heating element at said inlet end and causing the fire gases to flow upwardly through the passage to said outlet end, to heat the ore gravitating along opposite sides of the heating element progressively as the ore moves downwardly through said housing, while preventing contamination of said ore by said fire gases and preventing contamination of the fire gases by constituents of the ore;

means at the lower end for removing ore at a controlled rate, thereby to control the rate of flow of ore through said furnace and the period of exposure of the ore to said heating element;

and vapor withdrawal means positioned in said chamber at a predetermined level in said lower portion and communicating with said chamber on both sides of said heating element, but isolated from said passage, for removing vapor separated from said ore by heating, said vapor withdrawal means being disposed within some of said partitions and communicating with said hollow interior through the walls of said box structure.

9. An ore reduction furnace having, in combination:

an elongated, upright housing having refractory walls, open upper and lower ends, and a hollow interior extending between said ends and defining a furnace chamber of elongated rectangular horizontal cross-section;

a hopper on said upper end for receiving ore to be reduced and having an open bottom for directing the ore into said furnace chamber;

a vertically elongated heating element mounted in said furnace chamber in spaced relation with the walls thereof and extending from adjacent said lower end to adjacent said upper end, said heating element defining a serpentine passage extending back and forth within said furnace chamber generally in an upright plane, and longitudinally of said elongated cross-section, while progressing upwardly in said plane, from a lower inlet end to an upper outlet end, said passage beingsealed and isolated from said furnace chamber, and serving to divide the ore in said chamber generally into two flow paths along opposite sides of said element; said heating element comprising a lower portion resistant to the highest temperature levels in said furnace, and an upper portion resistant to lower temperature levels, said lower portion being constructed of sheet material as a sealed box structure having flat walls in spaced relation with the walls of said housing, and vertically spaced partitions mounted between said flat walls and defining a series of vertically spaced, elongated galleries for the flow of said fire gases, adjacent galleries communieating at alternating ends. to carry said fire gases back and forth along said serpentine path, and said upper portion being a tube communicating with the upper gallery in said structure and bending back and forth to continue said serpentine path from said structure to said outlet end;

means for supplying fire gases to said heating element at said inlet end and causing the fire gases to flow upwardly through the passage to said outlet end, to heat the ore gravitating along opposite sides of the heating element progressively as the ore moves downwardly through said housing, while preventing contamination of said ore by said fire gases and preventing contamination of the fire gases by constituents of the ore;

means at the lower end for removing ore at a controlled rate, thereby to control the rate of flow of ore through said furnace and the period of exposure of the ore to said heating element;

and vapor withdrawal means positioned in said chamber at a predetermined level in said lower'portion and communicating with said chamber on both sides of said heating element, but isolated from said passage, for removing vapor separated from said ore by heating.

10. An ore reduction furnace having, in combination:

an elongated, upright housing having refractory walls, open upper and lower ends, and a hollow interior extending between said ends and defining a.

furnace chamber of elongated rectangular horizontal cross-section;

a hopper on said upper end for receiving ore to be reduced and having an open bottom for directing the ore intosaid furnace chamber;

a vertically elongated heating element mounted in said furnace chamber in spaced relation with the walls thereof and extending from adjacent said lower end to adjacent said upper end, said heating element comprising a tube bending back and forth in an upright plane to form a series of oppositely facing U-shaped bends connected by straight sections of said tube and defining a serpentine passage extending back and forth within said furnace chamber while progressing upwardly in said plane, from a lower inlet end to an upper outlet end, said passage being sealed and isolated from said furnace chamber, and serving to divide the ore in said chamber generally into two flow paths along opposite sides of said element;

means for supplying fire gases to said heating element at said inlet end and causing the fire gases to flow upwardly through the passage to said outlet end, to heat the ore gravitating along opposite sides of the heating element progressively as the ore moves downwardly through said housing, while preventing contamination of said ore by said fire gases and preventing contamination of the fire gases by constituents of the ore,

means at the lower end for removing ore at a controlled rate, thereby to control the rate of flow of ore through said furnace and the period of exposure of the ore to said heating element;

14 prising a plurality of perforated pick-up tubes projecting into said chamber through the walls thereof and into the spaces between said straight sections of said heating element, and means for drawing vapor from said interior throughsaid tubes. 

1. An ore reduction furnace having, in combination: an elongated, upright housing having refractory walls, open upper and lower ends, and a hollow interior extending between said ends and defining a furnace chamber of elongated rectangular horizontal cross-section; a hopper on said upper end for receiving ore to be reduced and having an open bottom for directing the ore into said furnace chamber; a vertically elongated heating element mounted in said furnace chamber in spaced relation with the walls thereof and extending from adjacent said lower end to adjacent said upper end, said heating element comprising a sealed box structure of sheet material having partitions defining vertically spaced, elongated galleries communicating at alternating ends to define a serpentine passage extending back and forth in an upright plane, and longitudinally of said elongated cross-section, while progressing upwardly in said plane, from a lower inlet end to an upper outlet end, said passage being sealed and isolated from said furnace chamber, and serving to divide the ore in said chamber generally into two flow paths along opposite sides of said element, at least one of said partitions being hollow and having ports therein communicating with the furnace chamber outside said box structure; means for supplying fire gases to said heating element at said inlet end and causing the fire gases to flow upwardly through the passage to said outlet end, to heat the ore gravitating along opposite sides of the heating element progressively as the ore moves downwardly through said housing, while preventing contamination of said ore by said fire gases and preventing contamination of the fire gases by constituents of the ore; means at the lower end for removing ore at a controlled rate, thereby to control the rate of flow of ore through said furnace and the period of exposure of the ore to said heating element; and vapor withdrawal means positioned in said chamber at a predetermined level in said lower portion and communicating with said chamber on both sides of said heating element, but isolated from said passage, for removing vapor separated from said ore by heating, said vapor withdrawal means including at least one perforated pick-up tube disposed within said hollow partition.
 2. An ore reduction furnace as defined in claim 1 in which said box structure has holes in its walls opening into the hollow interior of the partition, said holes being tapered from relatively small outer ends to relatively large inner ends.
 3. An ore reduction furnace as defined in claim 1 in which said box structure has holes in its walls opening into the hollow interior of the partition, and the pick-up tube therein has perforations which open out of the pick-up tube away from said holes, to avoid straight-line flow of vapor to the pick-up tube.
 4. An ore reduction furnace having, in combination: an elongated refractory housing adapted for operation in an upright position and having an inlet opening in its upper end for receiving ore, an elongated hollow interior defining a chamber for the flow of ore downwardly through said housing, and a discharge opening in its lower end; an elongated heating element disposed in said housing in spaced relation with the walls thereof and extending from an inlet end adjacent said discharge opening, upwardly through said hollow interior to an outlet end, said housing defining two main flow paths on opposite sides of said heating element for gravity flows of ore introduced through said inlet opening, and said heating element defining a sealed passage isolated from said flow paths for a fluid heating medium introduced at said inlet End, said sealed passage extending back and forth across said hollow interior while progressing upwardly therethrough to provide prolonged residence time for said heating medium in said heating element, whereby the ore passing downwardly through said housing is heated progressively from a relatively low input temperature to a relatively high separation temperature as the ore approaches said outlet end; means at said discharge opening for removing ore therefrom at a controlled rate thereby to control the rate of flow of ore along said flow paths and the period of exposure of the ore to said heating element; and vapor withdrawal means in said housing at a predetermined level in the lower portion of said housing communicating with said hollow interior and both of said flow paths, but isolated from said sealed passage, for removing vapor separated from said ore by heating, said vapor withdrawal means being located substantially closer to said discharge opening than to said inlet opening and including a perforated pick-up member extending transversely across said hollow interior, and means for drawing vapor into said pick-up member from said hollow interior.
 5. An ore reduction furnace as defined in claim 4 in which said heating element comprises a continuous tube bending back and forth to form a series of oppositely facing U-shaped bends connected by straight sections of said tube, and in which said pick-up member is an elongated tube having a perforated inner end portion disposed between two of said straight sections.
 6. An ore reduction furnace as defined in claim 4 in which at least the lower portion of said heating element is a sealed box structure constructed of sheet material and having flat upright walls in spaced relation with the walls of said housing and vertically spaced partitions mounted between said flat walls and defining a series of vertically spaced, transversely extending galleries, adjacent galleries communicating at alternating ends to carry fire gases back and forth along said serpentine path.
 7. An ore reduction furnace as defined in claim 6 in which said perforated pick-up member is disposed within one of said partitions, and communicates with said interior through the sides of said box-like structure.
 8. An ore reduction furnace having, in combination: an elongated, upright housing having refractory walls, open upper and lower ends, and a hollow interior extending between said ends and defining a furnace chamber of elongated rectangular horizontal cross-section; a hopper on said upper end for receiving ore to be reduced and having an open bottom for directing the ore into said furnace chamber; a vertically elongated heating element mounted in said furnace chamber in spaced relation with the walls thereof and extending from adjacent said lower end to adjacent said upper end, said heating element defining a serpentine passage extending back and forth within said furnace chamber generally in an upright plane, and longitudinally of said elongated cross-section, while progressing upwardly in said plane, from a lower inlet end to an upper outlet end, said passage being sealed and isolated from said furnace chamber, and serving to divide the ore in said chamber generally into two flow paths along opposite sides of said element; at least part of said heating element being a sealed box structure of heat-resistant sheet material centrally disposed in the lower portion of said chamber and having vertically spaced partitions defining vertically spaced, transverse galleries communicating through connecting ports positioned in an alternating manner adjacent the opposite sides of said structure to cause said fire gases to flow back and forth while progressing upwardly through the box structure; means for supplying fire gases to said heating element at said inlet end and causing the fire gases to flow upwardly through the passage to said outlet end, to heat the ore gravitating along opposite sides of the heating element prOgressively as the ore moves downwardly through said housing, while preventing contamination of said ore by said fire gases and preventing contamination of the fire gases by constituents of the ore; means at the lower end for removing ore at a controlled rate, thereby to control the rate of flow of ore through said furnace and the period of exposure of the ore to said heating element; and vapor withdrawal means positioned in said chamber at a predetermined level in said lower portion and communicating with said chamber on both sides of said heating element, but isolated from said passage, for removing vapor separated from said ore by heating, said vapor withdrawal means being disposed within some of said partitions and communicating with said hollow interior through the walls of said box structure.
 9. An ore reduction furnace having, in combination: an elongated, upright housing having refractory walls, open upper and lower ends, and a hollow interior extending between said ends and defining a furnace chamber of elongated rectangular horizontal cross-section; a hopper on said upper end for receiving ore to be reduced and having an open bottom for directing the ore into said furnace chamber; a vertically elongated heating element mounted in said furnace chamber in spaced relation with the walls thereof and extending from adjacent said lower end to adjacent said upper end, said heating element defining a serpentine passage extending back and forth within said furnace chamber generally in an upright plane, and longitudinally of said elongated cross-section, while progressing upwardly in said plane, from a lower inlet end to an upper outlet end, said passage being sealed and isolated from said furnace chamber, and serving to divide the ore in said chamber generally into two flow paths along opposite sides of said element; said heating element comprising a lower portion resistant to the highest temperature levels in said furnace, and an upper portion resistant to lower temperature levels, said lower portion being constructed of sheet material as a sealed box structure having flat walls in spaced relation with the walls of said housing, and vertically spaced partitions mounted between said flat walls and defining a series of vertically spaced, elongated galleries for the flow of said fire gases, adjacent galleries communicating at alternating ends to carry said fire gases back and forth along said serpentine path, and said upper portion being a tube communicating with the upper gallery in said structure and bending back and forth to continue said serpentine path from said structure to said outlet end; means for supplying fire gases to said heating element at said inlet end and causing the fire gases to flow upwardly through the passage to said outlet end, to heat the ore gravitating along opposite sides of the heating element progressively as the ore moves downwardly through said housing, while preventing contamination of said ore by said fire gases and preventing contamination of the fire gases by constituents of the ore; means at the lower end for removing ore at a controlled rate, thereby to control the rate of flow of ore through said furnace and the period of exposure of the ore to said heating element; and vapor withdrawal means positioned in said chamber at a predetermined level in said lower portion and communicating with said chamber on both sides of said heating element, but isolated from said passage, for removing vapor separated from said ore by heating.
 10. An ore reduction furnace having, in combination: an elongated, upright housing having refractory walls, open upper and lower ends, and a hollow interior extending between said ends and defining a furnace chamber of elongated rectangular horizontal cross-section; a hopper on said upper end for receiving ore to be reduced and having an open bottom for directing the ore into said furnace chamber; a vertically elongated heating element mounted in said furnace cHamber in spaced relation with the walls thereof and extending from adjacent said lower end to adjacent said upper end, said heating element comprising a tube bending back and forth in an upright plane to form a series of oppositely facing U-shaped bends connected by straight sections of said tube and defining a serpentine passage extending back and forth within said furnace chamber while progressing upwardly in said plane, from a lower inlet end to an upper outlet end, said passage being sealed and isolated from said furnace chamber, and serving to divide the ore in said chamber generally into two flow paths along opposite sides of said element; means for supplying fire gases to said heating element at said inlet end and causing the fire gases to flow upwardly through the passage to said outlet end, to heat the ore gravitating along opposite sides of the heating element progressively as the ore moves downwardly through said housing, while preventing contamination of said ore by said fire gases and preventing contamination of the fire gases by constituents of the ore; means at the lower end for removing ore at a controlled rate, thereby to control the rate of flow of ore through said furnace and the period of exposure of the ore to said heating element; and vapor withdrawal means positioned in said chamber at a predetermined level in said lower portion and communicating with said chamber on both sides of said heating element, but isolated from said passage, for removing vapor separated from said ore by heating, said vapor withdrawal means comprising a plurality of perforated pick-up tubes projecting into said chamber through the walls thereof and into the spaces between said straight sections of said heating element, and means for drawing vapor from said interior through said tubes. 